The present invention relates to a paste container that is used in screen printing in which paste such as cream solder or conductive paste is printed on a board.
In an electronic parts mounting process, screen printing is used as a method for printing paste such as cream solder or conductive paste on a board. In this method, a mask plate in which pattern holes are formed at printing locations is set on a board and paste is printed on the board via the pattern holes of the mask plate by squeegeeing.
Among squeegeeing methods for screen printing, a method for using a closed type squeegee head is known. In this method, unlike the conventional screen printing in which paste is directly supplied onto a mask plate, a squeegee head storing paste inside is used. More specifically, the paste inside the squeegee head is pressurized in a state that a paste contact surface that is provided in the bottom surface of the squeegee head is in contact with a mask plate, whereby paste is squeezed into pattern holes of the mask plate through the paste contact surface. The pattern holes are filled in order with paste by sliding the squeegee head on the mask plate.
However, the screen printing using the above conventional closed type squeegee head has the following problems. Unlike in the conventional printing method in which paste is directly supplied onto the mask plate, in the closed type squeegee head paste is placed in the squeegee head in such a manner that paste is housed in a dedicated container such as a cartridge. Therefore, if the paste has been used up during the course of a printing operation, new paste is supplied by replacing the old dedicated container with a new one.
However, the dedicated container for the above conventional closed type squeegee head requires a high running cost because it is formed by molding resin into a long and narrow box shape. Further, paste remains inside the container and is discarded without being used, which means a waste of resources. These problems are factors of increasing the cost of screen printing. Incidentally, in performing screen printing, a preparatory operation is necessary in which paste is stirred to adjust its viscosity. However, the paste that is housed inside the box-shaped dedicated container cannot be stirred externally by a simple method. This means a problem that the viscosity adjustment cannot be performed easily.
Furthermore, the above paste container made of a resin film also has the following problem. A resin material for making the paste container is inexpensive and can be handled easily during manufacture. A lid of the paste container is made of a resin film on which a sticking layer is formed in advance that is coated with an adhesive material or coated with a laminate member to improve the ease of work of opening the lid that was bonded to the container by thermo-compression bonding. Therefore, in a state that paste is contained inside the container, the sticking layer is in contact with the paste. A component of the sticking layer may be eluted by a solvent component in the paste to change the composition of the paste or deteriorate printing quality.